Question

The fossil trilobite was originally
a. A reptile
b. An arthropod
c. An ave
d. An amphibian

Answer 1

Hint: Trilobites are extinct, joint-legged animals. They lived more than five hundred and twenty million years ago in the Cambrian Period. They had an exoskeleton with a three-lobed structure.

Complete answer:
> Option A:
Reptiles are Tetrapod vertebrates and ectothermic. They have very thick keratin scales. They are tough and have efficient lungs, which help them to survive in both water and land. They have a three-chambered heart having, two atria and one partially divided ventricle. They are cold-blooded. Option A is incorrect.

> Option B:
A hard exoskeleton and a segmented body are the characteristics of Arthropods. The head, thorax, and abdomen are the three segments in their body. In some arthropods, there is a cephalothorax i.e. the head and thorax are joined. They have characterized joint limbs and have cuticles made up of chitin. Trilobites were joint-legged animals. They had an exoskeleton with a three-lobed structure. They also had pleurae which are a pair of side lobes. Their structure resembles that of arthropods.

> Option C:
Aves are birds having front limbs modified into wings. The wings bear feathers which helps them to fly. An ordinary Ave will have a beak and feet known as claw and these are related to the kind of habitat they live in. They have hollow bones, making their body light, and allowing them to fly easily. They have a streamlined body too. Option c is incorrect

> Option D:
Amphibians are Tetrapod vertebrates. The young larvae have gills and the adults have lungs. Their heart is three-chambered and the nervous system has a complex structure.

Hence, the correct answer is option (B).

Note: The thorax of the trilobites has several articulated segments. Trilobites have many characteristics similar to arthropods and were not found after the Permian Period. Evolution has changed the structure of arthropods but the resemblance to Trilobites is clear.